What is an ETF?
An ETF is a form of index fund from standpoint of its goal: To provide a market benchmark return but at a minimal cost. In comparison Index funds are costly to trade and often ETFs can be traded commission-free.
However not all ETFs follow index funds methodology. To achieve index performance but with a minimal cost, you should invest in the largest, most widely traded ETFs on the market, which mimic well-known benchmarks and have history to prove it.